Effect of processing on the protein digestibility and mineral bioavailability of legumes

This study evaluates how processing methods, soaking/cooking, fermentation (e.g. tempeh), and protein coagulation (e.g. tofu), affect the nutritional profile, protein digestibility, and mineral bioavailability of faba beans, grey peas, yellow peas, and soybeans. Protein digestibility was assessed using in vitro digestion and o-phthalaldehyde (OPA) assay, whilst mineral bioavailability was estimated using phytate-to-mineral molar ratios and further evaluated using a Caco-2/HT29-MTX co-culture model measuring ferritin formation. Processing markedly influenced nutritional properties. Protein coagulation resulted in the highest protein content and degree of hydrolysis, indicating improved protein digestibility. Fermentation substantially reduced phytate levels across all crops, in some cases below detection limits, leading to lower phytate-to-mineral ratios compared with cooked and tofu products. Consistent with these estimates, higher ferritin formation was observed in cells exposed to digested fermented products than to tofu digesta. Processing also altered amino acid composition, reflecting structural modifications of proteins. Overall, the results demonstrate that processing modulates protein digestibility and mineral bioavailability of legumes. Fermentation shows potential to enhance mineral availability, whereas protein coagulation improves protein digestibility. These findings are based on in vitro and cell-based models and provide guidance for the development of nutritionally improved plant-based foods.